First things first.

Test the pressure. You will have two pressure readings. They must both be within specs.

It's been a while since I had the CIS system but the FIRST thing you have to do is get the pressure correct. A new pump doesn't mean anything if the fuel distributor isn't regulating the fuel properly.

If the fuel pressure is correct then check the engine for chain stretch/chain guide wear.

Pressure good and chain okay? Pull the injectors and check for spray patterns and flow. (I jump the relay in the fuse box to over ride the automatic fuel pump shut off, use a starter button to control the power) I use a baby food jar for each injector which allows me to compare the amount emitted.

The O2 sensor has very little to do with anything on the car. Don't believe me? You can completely disconnect the "computer" in the right side foot well (not the stupid "alarm" one but the one behind the kick panel) and the car will run the same.

I think tht bad injectors or incorrect pressure are most likely the culprit. I will have to check them this weekend and report back.

From past experience with my 84 500SEL ignition and fuel problems cause missfires which you can feel. If the engine runs smooth but lacks power, either there is a brake problem (not likely) or an exhaust problem. Cam timing could cause it but it would have to be from a 'gone bad' chain replacement. If you don't know the history of the car, you need to check the cam timing and the upper chain guides. If the guides are a dark brown color, they need to be replaced ASAP. If a chain guide brakes you will either spend a lot of time and money or junk the car. Usually most people WILL junk the car. That is how I got my car for $500.
How many miles are on the car?

Paul

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84 500 SEL (307,xxx miles)

Could be badly worn camshafts.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

Just a thought can a disused or dried out fuel pressure regulator contribute to the sluggish behaviour ?
regards
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the car only has 150k on it and from what i was told it was properly maintained. I actually found a sticker in the side door with the name of my Benz shop on it so I plan to call them and see what their records say about the car.

If I only had a nickle for each time I was told that...